"Mozilla and Foxconn have officially announced a partnership and confirmed that the two firms are developing at least 5 new devices, including a tablet computer. At a press conference today at Computex 2013 in Taipei, Li Gong, CEO of Mozilla Taiwan, and Young Liu, General Manager of Foxconn innovation Digital System Business Group, unveiled a new tablet prototype model designed for an unnamed OEM."

Chromebook runs a fully fledged operating system with a window manager and native apps on top which also happens to run web apps. Firefox OS is made in HTML5/JavaScript from the ground up, everything in there is a web page, there isn't a single line of native code besides the (hidden) browser. Even the window manager is written in JavaScript: